1. Field of the Invention
The present invention relates generally to a method of fabricating semiconductor packages and, more particularly, to a method of forming solder balls of semiconductor packages and semiconductor package structures using the same.
2. Description of the Related Art
Integrated circuit devices may be fabricated on a semiconductor wafer, cut into chips, assembled into packages, and utilized in electronic products. Semiconductor packages may support the integrated circuit (IC) chips physically, protect them from the influence of external environment, and provide electrical connection paths to the IC chips. Packaging technology may affect the price, performance, and/or reliability of a semiconductor product.
Various types of semiconductor packages are well known in this art. In one example semiconductor package, IC chips may be attached on one surface of a circuit substrate and solder balls acting as external terminals of the package may be mounted on another surface. Providing a solder ball arrangement on a surface of a circuit substrate may allow for increases in the number of input/output pins and the packaging density, and reductions in electrical signal paths, for example.
Solder ball attaching techniques are well known in this art. According to one conventional method, flux may applied to land patterns on the circuit substrate. Solder balls may be attached on the flux using a ball attaching apparatus. The solder balls may be melted via reflow and attached on the land patterns.
Although conventional solder ball attaching techniques are generally thought to be acceptable, they are not without shortcomings. For example, failures in solder ball attachment may occur. The solder balls may be furnished on the surface of the flux-applied land patterns using an automated apparatus. The likelihood of solder ball attachment failure may increase as the solder ball size is decreased to about 0.3-0.4 mm in diameter, for example. Further, the likelihood of solder ball attachment failure may increase as the number of solder balls is increased into the hundreds and even thousands, for example.
In the case of a ball pitch of less than or equal to 0.3 mm, for example, ball short circuit problems may occur due to a flux overflow phenomenon. The flux, which may be of a low viscosity and water-soluble, may tend to spread out of the land patterns. Therefore, portions of the flux applied to neighboring land patterns may stick together, and this may lead to short circuits between the solder balls, where the solder balls melted via reflow may contact each other.
Ball deformation problems may occur. During flux application, uneven flux may be skewed to one side of the land pattern. Uneven flux may cause the solder balls melted via reflow to be deformed.
Further, a layer of intermetallic compounds, resulting from metallic reaction and diffusion between a land pattern constituent (e.g., copper (Cu)) and a solder ball constituent (e.g., tin (Sn)), may adversely effect electrical reliability.